1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method for processing a color document image.
2. Description of the Related Art
Recently, computerization of information advances, and a system for computerizing a paper document by scanning using a scanner, storing the computerized information, and transmitting it to another apparatus has been widely popularized. In such a system, high compressibility for a computerized document is required for reducing a transmission cost. However, in a case where a text region and a photo region intermingle in a document image, when a user performs proper compression for the text region, an image quality comes to be good, but a compression ratio decreases. When a user performs proper compression for the photo region, a compression ratio is high but a text comes to deteriorate. Further, it is desired that computerized data has reusability capable of partially editing and high image quality in which image quality is not damaged even when the image is magnified or reduced.
To address these issues, Japanese Patent Application Laid-Open No. 2004-265384 discusses a method for attaining high compressibility, reusability, and high image quality of a document image. The method includes segmenting a computerized document image into a text region and a photo region, converting the text region, in which the reusability and high image quality are seriously considered, into vector data, performing Joint Photographic Experts Group (JPEG) compression on a region other than the text region, which can not be simply reproduced by vectorization, for example, the photo region, combining the vector data and the compression data acquired from each region, and outputting the combined data.
Japanese Patent Application Laid-Open No. 2004-265384 discusses a method for converting a region including the attribute of text, line, line drawing, or table into vector data. Further, Japanese Patent Application Laid-Open No. 2006-344069 discusses a method for, to expand the range of vectorization processing objects, vectorizing also an image having characteristics, for example, having a clear contour of an object image, i.e., a clear boundary of color, and a limited appearance color. Such an image is, for example, an illustration image. Hereinafter, such an image having a feature suitable for vectorization processing (for example, an illustration image) is referred to as “graphics” (or “a graphic image”). In addition, the method discussed in Japanese Patent Application Laid-Open No. 2006-344069 includes segmenting such a graphic image into color regions by a degree of color similarity, approximating a contour of each color region by an outline method, adding color information to vector data, and outputting the data.
On the other hand, since a photo region and graphics, such as an illustration image, have a similar characteristic in many case, it is difficult to accurately distinguish between a photo region and graphics in a document image, so that a photo region may be erroneously determined to be graphics. If an image processing apparatus vectorizes a photo region that is erroneously determined to be graphics, the image quality or compression ratio may decrease.